To keep the pages in my art journal from sticking together, I use parchment paper. In the states, parchment paper is sold at the grocery store in rolls. It's in the baking department near the aluminum foil and wax paper. It is usually white or brown. Put parchment paper in between the pages and put your pages/journal under heavy books overnight.

You can just keep re-using the paper, and any paint on the parchment could transfer to your page. The yellow on the page below was from used parchment. I don't mind, but you might.

It can take a few hours to a few weeks for an art journal page to be completely dry. It depends how many layers of acrylic paint and papers you have used. Other factors that influence drying time include humidity & temperature in your work space and storage area.

Hope this helps in your quest for unstickification.

Note: Read the comments for more details about the unsticking process!